The interpretation of speech reception threshold data in normal-hearing and hearing-impaired listeners: II. Fluctuating noise.

Following previous work [Smits and Festen. (2011). J. Acoust. Soc. Am. 130, 2987-2998] involving the interpretation of speech reception threshold (SRT) data in steady-state noise, the present study considers fluctuating noise. Whereas the SIIsteady function [i.e., the speech intelligibility index (SII) against SNR in steady-state noise] can be approximated by a simple linear function going from 0 to 1 between SNR = -15 dB to +15 dB, the SIIfluc function is a function over a broader range than 30 dB and its maximum lies at a SNR higher than +15 dB. The difference in shape between the SIIsteady and SIIfluc functions has several implications. It predicts a reduction in fluctuating masker benefit (FMB), or even a negative FMB, for higher SNRs for normal-hearing listeners. Experimental data confirm this prediction. Much of the reduction in FMB for hearing-impaired listeners may be attributed to the higher SRTs in steady-state noise for these listeners.